1. Field of the Invention
The present invention relates to a process for the preparation of foams characterized by carbodiimide and isocyanurate linkages. More particularly, the invention relates to the preparation of foams characterized by carbodiimide and isocyanurate linkages employing certain quaternary boron salts as catalysts for both the carbodiimide and isocyanurate reactions.
2. Prior Art
The preparation of rigid foams characterized by carbodiimide and isocyanurate linkages is well known in the art as evidenced by inter alia U.S. Pat. Nos. 3,645,923; 3,657,161; 3,717,596; 3,723,366; and 3,746,709. Generally, these foams are prepared by catalytically condensing an organic polyisocyanate (a) in the presence of a compound which promotes the carbodiimide reaction and a compound which promotes trimerization reaction or (b) in the presence of a compound which promotes both reactions.
U.S. Pat. No. 3,635,848 teaches the use of a coordination compound of an organic borate ester and an alkali or alkaline earth metal as a trimerization catalyst for organic polyisocyanates. There is no teaching of the use of the compounds of this patent as catalysts for the preparation of foams characterized by carbodiimide and isocyanurate linkages.
U.S. Pat. No. 3,697,485 teaches the use of a catalyst system comprising an organic orthoborate and an alcoholate or phenolate salt as a trimerization catalyst for organic polyisocyanates. There is no teaching of the use of the catalysts with carbodiimide-promoting compounds or that the catalysts promote the carbodiimide reaction. In fact, since the systems of this patent are primarily useful in the preparation of molded resins, the formation of carbodiimide groups, which would necessitate the generation of carbon dioxide, would be very undesirable for such an application.